Securing threaded backplate

[Thomas StauboParticipant @thomasstaubo12021]

I'm in the process of machining a backplate out of cast iron, for a new 5" chuck I have. This is for my Myford ML7, and the spindle nose is threaded as you know.

I have not had any problem with my chucks unscrewing, but it would be nice to have the possibility of running the lathe in reverse occasionaly. And I thought that I might as well make some sort of locking mechanism while I'm at it making the backplate.

I've tried searching for possible solutions. I've seen some (Schaublin?) use a clamping ring that compresses the chuck spigot onto the register, like this:

But I was thinking of utilising the collar that is next to the register on the Myford spindle, it's 1/4" wide and 40.9mm in diameter.

I can extend the backplate to act as a sleeve over that collar, then slit that sleeve part axially. Like this:

And then use a similar clamping ring, as in the first picture, to clamp and secure it to the spindle.

What do you think?

[Thomas StauboParticipant @thomasstaubo12021]

[MuzzerParticipant @muzzer]

I expect the backplate is typically cast iron ie not very elastic but even if it were steel, you'd have a job clamping it down onto the register on the nose of the spindle, assuming it is nice and parallel and a very close fit.

Perhaps a collar that is secured to the backplate but still has a small amount of free movement would be simpler – ie held captive to the backplate by 3-4 socket headed capscrews. Then it could tighten onto the spindle nose without having to distort the backplate. This could be pretty secure.

I'd be surprised if it hasn't been done before on Myfords etc.

Murray

[Thomas StauboParticipant @thomasstaubo12021]

Hi Murray. You are probably right about the stiffness. But Schaublin somehow managed to clamp the backplate onto the register without slitting it!!

A simpler version that I thought about also, is machining a ~7mm wide spigot with the same diameter (40.9mm) as the collar on the spindle. And then using a steel clamping ring to clamp half on the spindle collar, and half on the backplate. Like this:

(found at http://www.model-engineer.co.uk/forums/postings.asp?th=47650 )

Your idea of a collar that is secured to the backplate but still has a small amount of free movement, is a good idea. I too thought about bolting the clamping ring to the backplate, but didn't think of the captive mounting and leaving it free to move, to avoid distortion. I wonder how important that is…?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Thomas Staubo on 23/02/2017 08:13:49:

Hi Murray. You are probably right about the stiffness. But Schaublin somehow managed to clamp the backplate onto the register without slitting it!!

.

A very good point, Thomas

I suspect it's all down to the fine tolerancing of the Schaublin components.

… More photos here, for reference.

http://www.nielsmachines.com/en/schaublin-sold-schaublin-70-fn-niederhausen-swiss.html

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

An alternative method of locking might possibly be to convert a radial pressure from locking screw[s] into an axial force; which would then load the chuck screw thread.

MichaelG.

[not done it yetParticipant @notdoneityet]

I would not even countenance the idea, let alone try something, that may allow any (even minute) loosening of the backplate from the register. Fretting could destroy the register in no time at all.

If you actually need a lathe which operates in the opposite direction to normal, buy one with a suitable spindle, not a threaded one, is my advice.

I would think these 'extras' are still only 'belt and braces' protection against the possibility of a chuck unwinding on deceleration, not against possible intermittent cutting forces in the 'undoing' direction at high speed. I may be wrong, but that is my take on it.

[Roger Provins 2Participant @rogerprovins2]

The Asian 9×20 lathe that comes in many different colours and many badged names has a method to prevent the chuck coming off when in reverse,

See here.

Roger

[Thomas StauboParticipant @thomasstaubo12021]

Thanks for the input everyone!

Just to make it clear, I will not clamp on the register, but on the 1/4" wide collar to the left of the register.

[Jon GibbsParticipant @jongibbs59756]

+1 for Roger's suggestion. It looks a good idea – especially if the clip clamps around the back of the 1/4" collar.

My ML7 has a pretty reasonable gap between the headstock and the 1/4" collar.

The other way would be a washer and a draw-bar through the headstock but that obviously has a draw-back in that the bore is out of action.

Jon

[Jon GibbsParticipant @jongibbs59756]

As a post script, if you're wanting to replicate the Grip-tru capabilities in your new chuck if it hasn't got them already, have you considered an adjustable backplate at the same time?

This one is from Hemingway but is pretty simple to incorporate from scratch based upon this diagram.

HTH

Jon

[Thomas StauboParticipant @thomasstaubo12021]

Thanks!

This is a drawing to make my idea clearer:

[Thomas StauboParticipant @thomasstaubo12021]

It wouldn't be that often that I would want to run it in reverse, but one purpose is to screwcut internal threads by running the tool from left to right (to avoid crashing the tool in the bottom of a blind bore).

Roger's suggestion with the clip may be an alternative. Does it lock the chuck on, or does it only prevent it running off.

Michael, I can't picture how your solution would work:

An alternative method of locking might possibly be to convert a radial pressure from locking screw[s] into an axial force; which would then load the chuck screw thread.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Thomas Staubo on 23/02/2017 12:54:35:

Michael, I can't picture how your solution would work:

An alternative method of locking might possibly be to convert a radial pressure from locking screw[s] into an axial force; which would then load the chuck screw thread.

.

Thomas,

I was thinking of a spacer 'washer' between the chuck and that collar, which you identify with the red arrow.

… Contrived to make it adjustable in thickness; it would shift the chuck minutely forward, and lock the screw thread.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Thomas Staubo on 23/02/2017 09:29:31:

Just to make it clear, … the 1/4" wide collar to the left of the register.

.

MichaelG.

[MuzzerParticipant @muzzer]

I like the split collar concept if you have the means to make it. Looks a test of your slitting saw technique!

I try to design things to be as easy possible to make. One option might be to make the collar in 2 parts, connected by some form of pin or bolt. Would simplify the construction somewhat.

Murray

[Jon GibbsParticipant @jongibbs59756]

Why wouldn't you make the locking collar part of the female threaded register section of the chuck?

A simpler alternative, that's used for woodturning chucks to stop them unscrewing from a threaded nose, would be some spaced brass faced grub screws bearing down onto the outside of the 1/4" wide collar.

On woodturning chucks they usually bear down on the register (!) – but the TIR requirements are less strict of course. A more recent solution from Axminster which IMHO is just as dodgy is to have grub screws which bear into dimples drilled into the front of the register face – as here…

Jon

[John Stevenson 1Participant @johnstevenson1]

That will just jack it off the register face.

OK for wood butchers working to plus or minus a plank.

[John Stevenson 1Participant @johnstevenson1]

Posted by Jon Gibbs on 23/02/2017 10:10:15:

As a post script, if you're wanting to replicate the Grip-tru capabilities in your new chuck if it hasn't got them already, have you considered an adjustable backplate at the same time?

This one is from Hemingway but is pretty simple to incorporate from scratch based upon this diagram.

HTH

Jon

.

I know you often don't get a choice on how many screws hold a chuck but when the Grip-Tru type adjustable backplate is made why do they insist on still using 3 screws for adjustment.

Adjust three screws at 120 degrees is a right pain working out what is going to move what way.

Why don't they use 4 and mimic a 4 jaw chuck where you work in two sets of 2 jaws for adjustment.

If it was that easy they would make and sell 3 jaw independent chucks but they don't – wonder why ?

[Thomas StauboParticipant @thomasstaubo12021]

The grip-tru chuck with adjusting screws is a good idea, but I don't think I can incorporate that on my backplate now.

 

But if I'm not satisfied with the runout when I mount my chuck, or if I need extra precision, this is the method I would use:

Watch from 22:50

 

He has a slight clearance on the chuck register, and by loosening the clamping bolts he can bump the chuck so the workpiece runs true.

 

.

Edited By Thomas Staubo on 24/02/2017 08:12:27

[not done it yetParticipant @notdoneityet]

If it was that easy they would make and sell 3 jaw independent chucks but they don't – wonder why ?

Similar reasoning why nobody makes locking back plates for Myford lathes? Either simply not needed or not practical? I think the latter.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Stevenson on 23/02/2017 23:28:30:

I know you often don't get a choice on how many screws hold a chuck but when the Grip-Tru type adjustable backplate is made why do they insist on still using 3 screws for adjustment.

Adjust three screws at 120 degrees is a right pain working out what is going to move what way.

Why don't they use 4 and mimic a 4 jaw chuck where you work in two sets of 2 jaws for adjustment.

If it was that easy they would make and sell 3 jaw independent chucks but they don't – wonder why ?

.

John,

You raise some valid points there, but I think I can give a reasonable answer:

Three screws are used for 'kinematic' stability [cf. the three-legged milking stool]

… using four adjusters, although convenient, introduces the risk of instability.

MichaelG.

[Jon GibbsParticipant @jongibbs59756]

Posted by John Stevenson on 23/02/2017 23:28:30:

Posted by Jon Gibbs on 23/02/2017 10:10:15:

As a post script, if you're wanting to replicate the Grip-tru capabilities in your new chuck if it hasn't got them already, have you considered an adjustable backplate at the same time?

This one is from Hemingway but is pretty simple to incorporate from scratch based upon this diagram.

I know you often don't get a choice on how many screws hold a chuck but when the Grip-Tru type adjustable backplate is made why do they insist on still using 3 screws for adjustment.

Why don't they use 4 and mimic a 4 jaw chuck where you work in two sets of 2 jaws for adjustment.

Blimey, I hadn't looked that closely before but you're right – even the Hemingway version also has 3 adjusting screws.

I made my own knock-off of it with 4 adjusting screws although it still has 3 retaining screws.

Thomas,

Yes I've seen Stefan do it that way and it clearly works but somehow not as elegant if you're doing it from scratch IMHO.

Jon

[John Stevenson 1Participant @johnstevenson1]

Posted by Michael Gilligan on 24/02/2017 08:42:06:

Posted by John Stevenson on 23/02/2017 23:28:30:

I know you often don't get a choice on how many screws hold a chuck but when the Grip-Tru type adjustable backplate is made why do they insist on still using 3 screws for adjustment.

Adjust three screws at 120 degrees is a right pain working out what is going to move what way.

Why don't they use 4 and mimic a 4 jaw chuck where you work in two sets of 2 jaws for adjustment.

If it was that easy they would make and sell 3 jaw independent chucks but they don't – wonder why ?

.

John,

You raise some valid points there, but I think I can give a reasonable answer:

Three screws are used for 'kinematic' stability [cf. the three-legged milking stool]

… using four adjusters, although convenient, introduces the risk of instability.

MichaelG.

.

So a 4 jaw chuck with all the jaws tightened is unstable ?

I think all the books that advocate using a 4 jaw for greater gripping power need re-writing then ?

[Michael GilliganParticipant @michaelgilligan61133]

For the sake of completeness:

If a semi-permanent solution was required for "the Myford problem", it should be perfectly possible to secure a good backplate to the threaded spindle-nose [using e.g. Loctite 638] and machine it to replicate the popular flange-fixing arrangement.

MichaelG.

[obviously, the viability of this idea would depend upon individual circumstaces]

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